It is known that a laser module used for an optical transmission device or the like, has included a photodiode in the rear of a laser diode as a light source. For monitoring power output from the laser diode, optical power output to rearward of the laser diode is monitored by the photodiode. FIG. 15 is a diagram illustrating an example of the configuration of a laser module of the related art.
As illustrated in FIG. 15, a laser module 100 includes a laser diode (LD) 110, a lens 120, an isolator 130, a lens 140, a ferrule 150, and a photo diode (PD) 160, and is jointed to an optical fiber 200. The laser diode 110 emits laser light which is focused by the lens 120. The focused laser light then enter the isolator 130 which blocks laser light propagating in a direction different from a propagating direction from the lens 120 to the lens 140.
The laser light focused by the lens 120 enters the lens 140 to be further focused. The further focused laser light enters an optical fiber 200 which is joined to the laser module 100 via the ferrule 150. As described above, in the rear of the laser diode 110 the photo diode 160 is provided to receive the laser light emitted from the laser diode 110 in the opposite direction from the lens 120. In this manner, the output of the laser diode 110 is monitored by monitoring the laser light received by the photo diode 160 in the laser module of the related art.
In addition, there has been known an optical transmission device in which an optical coupler is disposed in front of a laser module. In the optical transmission device, a part of laser light emitted from the laser module is branched in the optical coupler. The optical transmission device monitors the output of the laser module by monitoring the optical power of the branched laser light. FIG. 16 is a diagram illustrating an example of an optical transmission device of the related art.
As illustrated in FIG. 16, an optical transmission device 2000 includes a laser module 100, an optical coupler 300, and a photo diode 400. The optical coupler 300 branches laser light emitted from the laser module 100 into main signal light and monitoring light. The monitoring light is received by the photo diode 400. In the optical transmission device 2000 of the related art, the output of the laser module 100 is monitored by monitoring the laser light received by the photo diode 400.
An example of techniques of the related art is disclosed in Japanese Laid-open Patent Publication No. 07-74343.